This invention relates to radiation emission devices in general, and in particular to radiation emission devices of the type which are frequently referred to as lasers. Lasers are generally characterized by an elongated envelope containing a material which can be raised from an initial energy state to a so-called excited energy state. The particular means used to excite the material in the envelope may vary. Thus, depending on the type of laser used, optical, electrical or chemical excitation means may be employed.
After excitation, radiation may be emitted spontaneously as the excited material returns to a more stable energy level and/or through stimulated emission. In either case, the wavelength of the radiation so emitted is a function of the quantum drop in the energy level of the excited material. This, in turn, depends upon the inherent characteristics of the material itself.
The radiation, which propagates at a constant wavelength, generally leaves the envelope via radiation transmission means disposed at both ends thereof. The radiation transmission means are typically translucent windows which are often, but not necessarily, inclined at an angle which optimizes a particular polarization of light. This inclination is usually referred to as Brewster's angle, and the windows so inclined are often characterized as Brewster's windows.
Lasers of the type described typically include reflection means such as concave mirrors located a predetermined distance beyond each translucent window. The mirrors are aligned such that the radiation emitted from a translucent window is reflected back into the envelope to stimulate the emission of a substantially increased amount of radiation which then passes through the opposite window. This increased radiation is likewise reflected back into the envelope by the other mirror, thereby increasing the emitted radiation even more. As the radiation is continuously reflected back and forth through the envelope, greater and greater amounts of radiation are produced. It is in this manner that the light energy used to initially stimulate the emission of radiation is "amplified" by the laser device. Of course, in order to enable the amplified radiation to escape therefrom, at least one of the mirrors is gnerally made only partially reflective.
Many different materials may be used to effect radiation emission, including certain members of the class of materials known as metals. Because the metals used in this type of laser must generally be transformed from a normally solid or liquid state, to a gaseous state in order to effect excitation, such lasers are frequently referred to as metal vapor lasers. It is thus clear that in metal vapor lasers, means must be provided which first vaporize the metal and then raise the vaporized metal from an initial energy state to an excited energy state.
In the past, this has sometimes been accomplished by providing, within the laser envelope, a pair of substantially flat electrodes--typically an anode and a cathode. Upon application of a predetermined voltage to the anode, electrical energy is conducted to the cathode by any suitable means, causing the cathode to heat up in a well-known manner. The heat of the cathode causes the metallic material confined in the envelope to become vaporized so that it can then be readily raised to an excited state.
This type of system has not been without concomitant drawbacks. For example, the use of a pair of electrodes as described above tends to create undesirable temperature gradients within the laser envelope resulting in uneven heating, and nonuniform vaporization and excitation of the metal. In addition, it is well known that the vaporized metal tends to condense on the translucent windows located at the ends of the elongated envelope, thereby rendering the windows relatively opaque, and hence less capable of transmitting radiation.
In the past, attempts to remedy this condensation problem have included the use of cataphoretic means for establishing an electric field within the laser envelope. The electric field is typically arranged to accelerate the vaporized metal ion away from the region nearest the translucent windows, thereby confining the vaporized metal to the more central portions of the envelope. However, many prior metal vapor lasers have required relatively complicated, cumbersome, and inefficient apparatus to accomplish both excitation and confinement of the metal.
Accordingly, it is a primary object of the invention to provide an improved device for emitting radiation. It is another object of the invention to provide a metal vapor laser which minimizes temperature gradients within the laser envelope, and therefore promotes uniform vaporization and excitation of the metal. It is also an object of the invention to provide, in a metal vapor laser, a configuration which achieves excitation and cataphoresis in a more efficient, effective and economical manner.
Many lasers of the prior art, in addition to the drawbacks mentioned above, are characterized by a configuration in which the envelope is prone to failure in handling or operation. It is thus a further object of the invention to provide a more durable laser configuration which is less likely to fail under such circumstances. Other objects, features and advantages of the invention, as summarized below, will be apparent upon reading the following detailed description in conjunction with the accompanying drawings.